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Masten: igniters/pintle injectors/injector dome

Posted by: stoffj - Fri Mar 30, 2007 12:58 am
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Masten: igniters/pintle injectors/injector dome 
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Post Masten: igniters/pintle injectors/injector dome   Posted on: Fri Mar 30, 2007 12:58 am
I am new to this site and thoroughly enjoy reading the updates:) As an aeronautics & astronautics undergrad and physics undergrad, I have done a lot of reading on bi prop regen engines. So, this leads me to a few questions I guess I don't know for MASTEN space systems!

Q1: from most of my readings in sutton's txt, ive seen pintle injectors mostly used with radiatively cooled or ablative chambers. yours is a regen chamber. how are you keeping the dome cooled?!? thermal coatings? is it the inherent recirculation zones that the pintle does? how does your dome not melt????

Q2: your torch igniter from the video i saw is a short 3-5 sec igniter instead running during the full duration like the earlier augmented spark igniters in NASA in the huzel and huang txts. how does the exhaust gases not melt or burn out the injector while the engine is running and the exhuast gases go up into the igniter?

hope these are reasonable learning questions to ask. congrats so far on the engine success! anxiously waiting undergrad:O)

~james


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Post Re: Masten: igniters/pintle injectors/injector dome   Posted on: Fri Mar 30, 2007 5:42 am
James,
stoffj wrote:
I am new to this site and thoroughly enjoy reading the updates:) As an aeronautics & astronautics undergrad and physics undergrad, I have done a lot of reading on bi prop regen engines. So, this leads me to a few questions I guess I don't know for MASTEN space systems!


Never be afraid to ask questions. We can't always give out technical answers, especially due to ITAR considerations (not everyone on this list is a US person, alas), but when we can, we will.

Quote:
Q1: from most of my readings in sutton's txt, ive seen pintle injectors mostly used with radiatively cooled or ablative chambers. yours is a regen chamber. how are you keeping the dome cooled?!? thermal coatings? is it the inherent recirculation zones that the pintle does? how does your dome not melt????


The head end (aka dome) is also regen cooled. But as you guessed, the head end region doesn't see anywhere near as much heat flux as other parts of the chamber. You could probably get away with doing something else (like thermal coatings, or just plain radiative/heatsink cooling), but in our particular setup having that area regen cooled actually makes the design easier, not harder.

Quote:
Q2: your torch igniter from the video i saw is a short 3-5 sec igniter instead running during the full duration like the earlier augmented spark igniters in NASA in the huzel and huang txts. how does the exhaust gases not melt or burn out the injector while the engine is running and the exhuast gases go up into the igniter?


The real danger isn't hot gasses, but hot *fast moving* gasses. You could in theory shut the igniter off, and just let it stagnate--since the igniter is pressure tight, there's nowhere for the gas to flow, so it won't actually get that hot. But for other reasons, we run a purge of sorts through the ignitor during the firing. Just enough gas flow to guarantee that the igniter chamber is slightly higher pressure than the main chamber, so the hot gasses can't "backwash" into the igniter.

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hope these are reasonable learning questions to ask. congrats so far on the engine success! anxiously waiting undergrad:O)


Hope that was helpful.

~Jon Goff


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Post regen dome?!   Posted on: Fri Mar 30, 2007 5:49 am
oh wow, thanks! i guess ive never seen a pintle dome be regen cooled. now that you mention purging the igniter, i recall reading that someone else was purging their thruster after running, i guess that would be for the same case, it is small thruster itself anyway. thanks again!

respectfully,

james


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Post oh....purging   Posted on: Fri Mar 30, 2007 6:22 am
so, they use one of the propellants or pressure gas (pressure feed system (He)) to purge the igniter chamber? is that enough to keep the igniter chamber pressure greater than the thruster chamber pressure? im thinking of something like a thruster has 300-500 psi and an igniter to have a greater chamber pressure? then again if i remember correctly, pressure spheres have something like a 4500psi rating. if thats the case, what is the natural expanding pressure of of typical gases like He and Nitrogen? I cant seem to find or recall this. I know nitrous oxide (oxidizer) expands naturally at something like 750psia for rocketry hybrid motors. oh.. and if it is a pressure medium that is purging the igniter, does it affect the mixture in the main thruster? i know that helium is inert, but does it do anything to performance?

respectfully,

james


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